The 25-year-old world number eight's second victory at the 250 event in the south of France brought his career tally of titles on the tour to nine.
"Adrian is always a tough player to face, for anyone. It's a great feeling to win again, I'm very happy with my week," Auger-Aliassime said.
Auger-Aliassime did not face a break point as he put on a clinical display to down the home favourite Mannarino in just over an hour and a half on court.
After a fast start, which sealed him the opening set, the match tightened up as the second frame ground towards a tie-break.
Down 2/4 in the breaker, Auger-Aliassime dropped the hammer to win five consecutive points and seal the victory.
En route to the championship match, the former world number five beat three-time Swiss Grand Slam winner Stan Wawrinka, as well as locals Arthur Fils and Titouan Droguet.
The triumph, which moved him ahead of Milos Raonic as Canada's most succesful men's player in the Open era in terms of titles, ensured Auger-Aliassime will move up to sixth in the next ATP rankings update.
